Typically, to steer guided projectiles, such as missiles or other airborne munitions, aerosurfaces or reaction-control systems (e.g., systems that employ nozzles or valves to release a fluid or gas) are actuated. For example, guided munitions may be steered by using electric actuators, powered by onboard batteries, to drive the aerosurfaces through mechanical linkages. These actuators, batteries, and linkages contribute substantially to a round's launch weight and occupy valuable (and scarce) onboard volume that could otherwise be used for additional payload or eliminated to extend the range of the projectile. Mechanical linkages also have a relatively high risk of failure under launch loads, as the munitions experience extreme launch accelerations and velocities. In addition, battery storage life may limit the amount of time that such systems may be stored, i.e., the systems may require periodic maintenance to recharge or replace the batteries. This may also affect operational readiness by minimizing up-time and increasing the logistics burden.
For their part, reaction-control systems typically employ either compressed gas stored onboard in pressure vessels prior to launch (known as “cold-gas systems”), or solid gas generators that generate the compressed gas subsequent to launch (for example through a combustible fuel that is ignited). Traditional cold-gas systems are massive and limited in available impulse. They generally require large and heavy storage tanks, which limit their use in guided projectiles. Solid gas generators are also large, generate heat internal to the round that may adversely impact other components, are impulse-limited, have additional ignition requirements, and create a high risk of jamming components of the reaction-control system with accumulated combustion products and residues.
In conventional projectiles, pneumatic actuators are large and heavy, and may not survive extreme operational environments. Hydraulic actuators generally require surge suppression. They too are large and heavy, and may have slow response times. Piezoelectric actuators tend to have limited force and displacement, require high voltages, and experience problems due to induced currents and hysteresis. Similarly, electromagnetic actuators may have insufficient structural strength, and also experience hysteresis. Shape memory alloy actuators typically have insufficient displacement, are affected by temperature fluctuations, and experience hysteresis.